Strength and elastic modulus enhancement in Mg-Li-Al matrix composites reinforced by ex situ TiB2 particles via stir casting

A novel Mg^(-1)0Li-3Al(wt.%,LA103)matrix composite reinforced by ex situ micron TiB_(2) particles was developed in the present study.The ball milling and cold pressing pretreatment of the reinforcements made it feasible to prepare this material under stir casting conditions with good dispersion.The microstructure and mechanical properties of the composites prepared by different pretreatment methods were analyzed in detail.The TiB_(2) particles in the Al-TiB_(2)/LA103 composite using the pretreatment process were uniformly distributed in the microstructure due to the formation of highly wettable core-shell units in the melt.Compared with the matrix alloys,the Al-TiB_(2)/LA103 composite exhibited effective strength and elastic modulus improvements while maintaining acceptable elongation.The strengthening effect in the composites was mainly attributed to the strong grain refining effect of TiB2.This work shows a balance of high specific modulus(36.1 GPa·cm^(3)·g^(-1))and elongation(8.4%)with the conventional stir casting path,which is of considerable application value.

Microstructure evolution and enhanced fatigue behavior in the Mg-10Li-5Zn-0.5Er alloys micro-alloyed with Yb

In this paper,(0.2-1 wt%)Yb was added to improve the tensile properties and high-cycle fatigue behavior of the as-cast and as-extruded Mg-10Li-5Zn-0.5Er alloys.It is found that Yb mainly affects the mechanical properties of the alloy by changing the grain size,type and morphology of the second phases.Yb mainly exists in the formation of Mg_(2)Yb and Mg-Zn-Yb phases in the metallographic structure.With the addition of Yb,the grains are refined and these Yb-containing phases replace the large-sized MgLiZn phase to be enriched at the grain boundaries.While the addition of excess Yb reduces the number of small-sized MgLiZn phases in the grain,thus reducing the alloys’mechanical performance.After extrusion,the small-sized MgLiZn phase is refined and the number increases,which effectively improves the tensile and fatigue strength of the alloy.The fatigue strength is mainly affected by the number and morphology of the second phase,positively correlated with the strength.Balanced in grain size and number and size of second phases,the extruded alloy with 0.2Yb added exhibits excellent mechanical properties with the yield strength,ultimate tensile strength and elongation of 292 MPa,303 MPa and 11.7%,and an fatigue strength of 130 MPa.

Atlantic blocking events in a simplified nonlinear baroclinic model for local finite-amplitude wave activity

为研究北大西洋阻高的形成机制,本文在局部有限振幅波活动(LWA)框架下进行了一系列数值实验.采用的数值模型能显式地描绘出两种重要的大气内部动力过程,即非线性纬向位涡通量和Rossby波包传播.模拟结果显示,这两种动力学过程均是形成大西洋阻高的重要机理.具体地,非线性纬向位涡通量和Rossby波包传播,分别是大西洋阻高南部和北部LWA形成的主导因子.因此,本研究综合了前人关于大西洋阻高的研究成果,为其形成机理提供了新的认识.

Effect of Y and Gd content on the microstructure and mechanical properties of Mg-Y-RE alloys

In the application of WE43,it is found that Y_(2)O_(3)inclusion formed in the process of casting seriously reduced the mechanical properties of the products.The reduction of the mechanical properties is even more distinct when it comes to the application in the thin walled complex-precision castings.In order to decrease the Y_(2)O_(3)inclusions,Gd element was used to replace part of the Y element in Mg-Y-RE series alloys.The effect of Y content(Mg-x Y-1Gd-2Nd-0.5Zn-0.5Zr)and Y/Gd ratio(Mg-x Y-(5-x)Gd-2Nd-0.5Zn-0.5Zr)on the microstructure and mechanical properties of Mg-Y-RE alloys were investigated in this paper.With decreasing Y content,the grain size of the alloys increased,both ultimate tensile strength(UTS)and yield strength(YS)of alloys decreased monotonically.Replacing part of Y content with Gd and keeping the total rare earth content unchanged,the low Y content Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy showed the same mechanical properties as the high Y content Mg-4Y-1Gd-2Nd-0.5Zn-0.5Zr alloy at both room and elevated temperatures.After solution treatment at 525°C for 8 h and aging treatment at 225°C for 10 h,the UTS,YS and elongation(ε)of Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy reached 281.7 MPa,198 MPa and 11.1%at room temperature,and 216.7 MPa,171.6 MPa and 16.1%at 250°C.The new low Y content Mg-2Y-2Nd-3Gd-0.5Zn-0.5Zr alloy is expected to replace the high Y content WE43 alloys,which can be used in the complex thin-walled parts of aviation products.

High temperature mechanical behavior of low-pressure sand-cast Mg-Gd-Y-Zr magnesium alloy

The aim of this work is firstly to optimize T6 heat-treatment of low-pressure sand-cast Mg-10Gd-3Y-0.5Zr alloy,and then systematically investigate the mechanical behavior of the T6-treated alloy from room temperature to 300℃.It turned out that the optimum T6 heat-treatments for the tested alloy are 525℃×12 h+225℃×14 h and 525℃×12 h+250℃×12 h which integrated age-hardening and tensile properties into account,respectively.The strength of the T6-treated alloy indicates obvious anomalous temperature dependence from room temperature to 300℃,namely both ultimate tensile strength and yield strength of the tested alloy firstly increase with tensile temperature,and then decrease as temperature increases further.Elongation increased with temperature monotonously.The tensile fracture mode of the tested alloy changes from transgranular fracture to intergranular fracture with the increasing of test temperature.

Microstructure evolution of semi-solid Mg-10Gd-3Y-0.5Zr alloy during isothermal heat treatment

In this study,the microstructure evolution of semi-solid Mg-10Gd-3Y-0.5Zr alloy during isothermal heat treatment has been investigated.The results show that primary particles coarsen continuously during the holding.Coarsening rate decreases with the increase of isothermal temperature.When isothermal temperature increases from 600℃ to 620℃,the dominant mechanism for coarsening changes from particle coalescence to Ostwald ripening.Equiaxed as-cast microstructure is beneficial to the semi-solid microstructure after isothermal heat treatment,which brings about the refinement and spheroidization of primary particles,and shortening of holding time.Significant modification of second phases can also be achieved after isothermal heat treatment,due to its unique solidification process.The optimum processing parameters for Mg-10Gd-3Y-0.5Zr alloy in isothermal heat treatment are isothermal temperature of 610℃-620℃ and holding time of 20-40 min.

Microstructure and mechanical properties of repair welds of low-pressure sand-cast Mg?Y?RE?Zr alloy by tungsten inert gas welding

The sand castings of Mg-Y-RE-Zr series alloys are widely utilized in the large scales and complex shapes in the aerospace industry,as a result of which there are always some cast defects in the products. In this study, the feasibility of repair welding of sand-cast Mg-4 Y-3 RE-0.5 Zr alloy by tungsten inert gas(TIG) welding was scrutinized with different welding currents from 150 to 210 A. The results indicated that defect-free repaired joints with good appearance could be acquired at 170 and 190 A. Interestingly, the grain size of the fusion zone(FZ) was refined initially and then increased with the linear increment of welding current. Because at the higher heat inputs, although the cooling rate of the molten pool was reduced, substantial constitutional supercooling for the grain refinement was attained after the Zr particles were transformed into Zr solutes. The tensile strength of the repaired joint at 170 A was 195 MPa with the maximum joint efficiency of 87.8%, and the elongation reached to 124.4% of the sand-cast base material(BM). However, serious grain coarsening and continuous eutectic structures generated in heat-affected zone(HAZ) above 190 A resulted in the weakening of the joint due to the brittle intergranular fracture.

High-cycle fatigue behavior of Mg-8Li-3Al-2Zn-0.5Y alloy under different states

In this study,the tensile and high-cycle fatigue properties of as-cast,solid solution treated and as-extruded Mg-8Li-3Al-2Zn-0.5Y alloy are investigated.The results show that the yield strength and ultimate tensile strength of as-cast alloy is 198.1 MPa and 222.5 MPa,which are improved to 274.7 MPa and 321.7 MPa,282.4 MPa and 319.3 MPa after solid solution and extrusion treatment,respectively.The high-cycle fatigue strength(at 10^(7)cycles,R=-1)of as-cast studied alloy is 65 MPa,which is improved to 90 MPa and 105 MPa after solid solution and extrusion treatment,respectively.The improvement of fatigue property of the solid solution treated alloy is mainly due to the lattice distortion caused by solid solution hindering the crack propagation.However,the improvement of fatigue property of the as-extruded alloy is mainly due to that the refined grains,stacked dislocations and dispersed secondary particles impede the crack propagation.

Realizing the purification and grain refinement of Mg-Gd-Y alloy by one-step flux refining

In the conventional melt preparation of magnesium rare-earth(Mg-RE)alloys,the repeated heating/cooling process involved in grain refinement and flux refining usually prolongs the preparation period and aggravates melt oxidation.In this work,the purification and grain refinement of Mg-9Gd-3Y(GW93)alloy was simultaneously realized by one-step refining at 740℃ by using a self-developed compound flux.The results show that,only after holding for 10 min,the inclusion content of the alloy is reduced by 81%to 0.29%,while the grain size is reduced by 84%to 119μm.A physical model depicting the interactions between compound flux and alloy melt was proposed based on thermodynamic calculation and microstructure observation.The grain refinement mechanism has been analyzed by considering the presence of Zr particle(Zr_(p))and Zr solute(Zr_(s)).In addition,the generated RECl_(3) was found to be readily absorbed by the flux,decreasing the surface tension and promoting the purification efficacy of the flux,which plays an important role in the promoted elongation of the as-cast Mg-9Gd-3Y-0.5Zr(GW93K)alloy.This work presents a unique prospect in simplifying the melt preparation of Mg-RE alloy with a promoted quality.

Recent advances in the detection and removal of heavy metal ions using functionalized layered double hydroxides:a review

Heavy metal pollution is one of the most severe environmental problems,possessing high ecotoxicity and health risk.Therefore,it is important to develop effective methods and corresponding materials for the detection and removal of heavy metals.Recent studies reveal the great potential of layered double hydroxides(LDHs)in detecting and removing heavy metals owing to their designable structure and tunable surface composition.In this review,we majorly discuss the recently adopted detection and removal of heavy metal ions based on LDHs.This review starts with an introduction of the structural characteristics and functionalization of LDHs.Then,the sensing tactics and mechanisms are introduced regarding LDHbased heavy metal ion detection.Based on the type of interaction,the removal of heavy metal ions with LDHs is summarized into two categories:reversible adsorption and irreversible mineralization.This review ends with a discussion on the challenges and future trends of LDH-based detectors and adsorbents for heavy metal ions.

Plastic deformation and heat treatment of Mg-Li alloys:a review

As the lightest structural metallic materials,Mg-Li alloys have a bright development prospect in the fields of aerospace,weapon equipment,electronic technology and transportation.In this paper,the research progress of deformation processing and heat treatment of Mg-Li alloys is reviewed,with particular emphasis on the factors affecting the plastic deformation,the effects of plastic deformation on microstructural evolution and mechanical properties,and the heat treatment behavior of Mg-Li alloys.The problems existing in the scale application of Mg-Li alloys are pointed out,and the research focus of Mg-Li alloys in the future are also prospected.

Microstructural evolution,mechanical properties and corrosion behavior of as-cast Mg-5Li-3Al-2Zn alloy with different Sn and Y addition

Influences of Sn and Y on the microstructure,mechanical properties,and corrosion behavior of as-cast Mg-5 Li-3 Al-2 Zn(LAZ532)alloy were investigated.The addition of Sn and Y refines grains and results in the formation of Mg2 Sn and Al2 Y phases,thus improving the mechanical properties of alloy by second phase strengthening and grain refinement strengthening.As-cast LAZ532 alloy shows typical filiform corrosion morphology,and the addition of Sn and Y does not change the corrosion mode of alloy.Ascast LAZ532-0.8 Sn-1.2 Y alloy shows excellent mechanical properties with yield strength of 166.2 MPa,ultimate tensile strength of 228.6 MPa and elongation of 14.8%,and exhibits the best corrosion resistance with the smallest corrosion current density and the lowest anodic dissolution rate.

Effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy

This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5 Y（wt%） alloy, which was prepared by casting, and then homogenized and rolled at 200℃. The rolling process was conducted with 10% reduction per pass and five different accumulated strains, varying from 10% to 70%. The results indicate that the as-cast and as-rolled Mg-8Li-3Al-2Zn-0.5Y alloys are composed of α-Mg, β-Li, AlLi and Al;Y phases. After rolling process,anisotropic microstructure was observed. a-Mg phase got elongated in both rolling direction and transverse direction with the addition of rolling strain. Consequently, the strength of the alloy in both directions was notably improved whereas the elongation declined, mainly caused by strain hardening and dispersion strengthening. The tensile properties of the as-rolled alloys in the RD, no matter the YS, UTS or the elongation, are higher than those of the TD due to their larger deformation strain and significant anisotropy in the hcp α-Mg phase. In addition, the fracture and strengthening mechanism of the tested alloys were also investigated systematically.

Microstructure and mechanical properties of sand-cast Mg-6Gd-3Y-0.5Zr alloy subject to thermal cycling treatment

This work was undertaken to investigate the microstructural evolution, mechanical properties and fracture behavior of sand-cast Mg-6 Gd-3 Y-0.5 Zr(GW63) alloy subject to thermal cycling treatment. In order to simulate the thermal cycling under extreme service conditions(space or moon environments), the sand-cast and T6 treated GW63 alloys were subjected to thermal cycling treatment which consists of deep cryogenic-elevated temperature cycling treatment(DCET) and deep cryogenic cycling treatment(DCT). Results indicate that there are significant gains in yield strength(YS) and ultimate tensile strength(UTS) of the sand-cast GW63 alloy after DCET, whereas the T6 state alloy undergoes a different variation in mechanical properties. However, no appreciable influence is revealed on the mechanical properties of the tested GW63 alloys after DCT. Meanwhile, the DCT and DCET have no obvious effects on the fracture morphology. The DCT enhances the precipitation kinetics via providing favorable nucleation sites for the precipitation of second phases. The elevated temperature process of DCET plays a crucial role in improving the aging-hardening responses and releasing the stress concentration brought by DCT to a great extent, leading to overcome the obstacle of essential phase transformation. The changes in mechanical properties are primarily attributed to the phase transformation of the studied alloys during DCET.

Effect of Different Ageing Processes on Microstructure and Mechanical Properties of Cast Al–3Li–2Cu–0.2Zr Alloy

The effect of different ageing processes on microstructure and mechanical properties of cast Al–3 Li–2 Cu–0.2 Zr alloy was investigated using transmission electron microscopy and tensile tests. The results showed that the mean size of δ′-Al3 Li particles and the number density of Cu-rich precipitates both increased with increasing ageing temperature from 150 to 190 °C for 24 h, resulting in increasingly high strength. In contrast, the ductility deteriorated with the increase in ageing temperature as a result of the intensified planar slip. The duplex low-to-high ageing treatment(120 °C for 6 h followed by 160 °C for 24 h) was shown to be beneficial to the ductility compared with the corresponding single-stage ageing treatment(160 °C for 24 h). The reduced slip length induced by the precipitation of θ′-Al 2 Cu phases was found to be mainly responsible for this ductility improvement.

Effect of Zn Addition on the Microstructure and Mechanical Properties of Cast Mg-10Gd-3.5Er-xZn-0.5Zr Alloys

In this work,the effects of Zn content(0-2 wt%)on microstructural evolution and mechanical properties of cast Mg-10Gd-3.5Er-0.5Zr alloys are studied.The results show that the as-cast Mg-10Gd-3.5Er-xZn-0.5Zr alloys are mainly composed of Mg matrix and secondary(Mg,Zn)3(Gd,Er)phases distributed along grain boundaries.With the increase in Zn content,the volume fraction of secondary(Mg,Zn)3(Gd,Er)phases increases and the grains get refined.In the process of solid solution treatment,Zn addition can lead to the formation of long-period stacking ordered(LPSO)structures and the volume fraction of LPSO structures increases with Zn content.In addition,the Zn addition can reduce the vacancy formation energy and accelerate the diffusion rate of RE elements in Mg matrix.Because of the comprehensive effect of secondary phases and the accelerated diffusion rate,the base alloy and 2Zn alloy have less grain growth after solid solution treatment than that of the 0.5Zn alloy and 1 Zn alloy.The precipitation process is also accelerated by enhanced diffusion rate.At room temperature(RT),the strengthening effect of β’+β1 precipitates is more effective than that of LPSO structures,so the peak-aged 0.5Zn alloy exhibits the most excellent mechanical performance at RT,with yield strength of 219 MPa,ultimate tensile strength 296 MPa and elongation of 6.4%.While LPSO structures have stronger strengthening effect at elevated temperature than that of β’+β1 precipitates,so the 1Zn alloy and 2Zn alloy have more stable mechanical performance than that of the base alloy and 0.5Zn alloy with the increase in tensile temperature.

Microstructural Characteristics and Mechanical Properties of Cast Mg–3Nd–3Gd–xZn–0.5Zr Alloys

The microstructure,aging behavior and mechanical properties of cast Mg–3Nd–3Gd–x Zn–0.5Zr(x=0,0.5,0.8,1 wt%)alloys are investigated in this work.Zn–Zr particles with different morphologies form during solution treatment due to the additions of Zn.As the Zn content increases,the number density of Zn–Zr particles also increases.Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior.In the peak-aged Zn-free alloy,β′′phases are the key strengthening precipitates.When 0.5 wt%Zn is added,besidesβ′′precipitates,additional fineβ_(1)precipitates form.With the addition of 0.8 wt%Zn,the peak-aged 0.8Zn alloy is characterized by predominantly prismaticβ_(1)and scanty basal precipitate distributions.The enhanced precipitation ofβ_(1)should be primarily attributable to the presence of increased Zn–Zr dispersoids.When Zn content further increases to 1 wt%,the precipitation of basal precipitates is markedly enhanced.Basal precipitates andβ_(1)phases are the key strengthening precipitates in the peak-aged 1Zn alloy.Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt%Zn addition,whose yield strength,ultimate tensile strength and elongation are 179 MPa,301 MPa and 5.3%,respectively.

Effects of processing parameters and addition of flame-retardant into moulding sand on the microstructure and fluidity of sand-cast magnesium alloy Mg-10Gd-3Y-0.5Zr

In this study, the effects of processing parameters（such as pouring temperature and mould pre-heating temperature） and flame-retardant content on the microstructure and fluidity of sand-cast magnesium（Mg） alloy Mg-10Gd-3Y-0.5Zr（GW103K） were systematically investigated. It was found that the increase of pouring temperature leads to coarsened microstructure and decreased fluidity of sand-cast GW103 K alloy. Increase of mould pre-heating temperature incurs coarsening of as-cast microstructure and increase of fluidity. The addition of flame-retardant into moulding sand has a negligible influence on the microstructure of sand-cast GW103 K alloy. With the increase in flame-retardant content,fluidity of the alloy initially increases and then decreases. The optimized process parameters and flameretardant addition were obtained to be pouring temperature of 750？C, mould temperature of 110？C, and flame-retardant addition of 1%. The fire retardant mechanism of moulding sand was determined.

The opposite effect of β_(1)/ β″ on the ductility of aged Mg-3Nd-3Gd-0.2Zn-0.5Zr alloy

1.Introduction Magnesium alloys containing rare earth elements(Mg-RE al-loys)are attractive structural materials for aerospace,defense,and automotive industries due to their relatively high strength,low density,and good castability[1-4].For casting Mg-RE alloys such as Mg-Nd,Mg-Gd,and Mg-Gd-Y,their high performance is mainly ascribed to a significant precipitation strengthening[5-7].